1. Field of the Invention
This invention relates to a controller of an ink jet head for ejecting ink droplets to a record medium for printing, a control method of an ink jet head, and an ink jet record apparatus.
2. Description of the Related Art
An ink jet printer causes ink droplets ejected from an ink jet head to hit printer paper that is moving relative to the ink jet head, thereby forming any desired image on the print paper. Known as such an ink jet head is a head including a plurality of nozzles for ejecting ink droplets, a plurality of pressure chambers communicating with the nozzles, and a plurality of actuators placed so as to correspond to the pressure chambers. When an actuator is driven, the volume of the pressure chamber corresponding to the actuator decreases and ink as much as the decreased volume is ejected as an ink droplet from the nozzle.
Ink is held by capillarity in an ink flow passage including a nozzle and a pressure chamber, and an ink meniscus is formed in the nozzle. When an ink droplet is ejected, pressure produced when the actuator changes the volume of the pressure chamber remains in the ink flow passage. Thus, the ink meniscus in the nozzle vibrates accordingly. The vibration frequency of the meniscus depends on pressure wave propagation time T in the ink flow passage. The propagation time T is determined by length L of the ink flow passage. That is, letting the pressure wave propagation velocity be a, the propagation time T is determined as T=L/a.
The meniscus shape may be disordered because of the affect of the shape of the ink flowpassage, etc., and the effect of the remaining pressure in the ink flow passage produced by ejecting the ink droplet, etc., resulting in worsening the hit accuracy of the ink droplet. Then, JP-A-2001-277507 (FIG. 2) discloses an art of appropriately selecting the ejection timing at which the remaining vibration can be restricted in response to the ejection situation of ink droplets and ejecting an ink droplet in a predetermined cycle, thereby enhancing the hit accuracy of the ink droplets. Accordingly, the ink droplet ejected from the nozzle can be always caused to hit a constant position regardless of the ejection situation of the ink droplets.